Alajo, one of the numerous metropolises within Accra, is located in the northern part of the capital. It is approximately 45minute drive from Korle Bu Teaching hospital. According to the census bureau the total population is about 500000 thousand as at 2000. With this significant number it is estimated that the population can raise to about 800000 thousand people by the end of 2006. This is due to the high birth rate in the area and increase in the number of peoples migrating from the rural areas to the capital city. Alajo is susceptible to occasional flooding during heavy rainfall as a result of the nature of landscape, poor road network, poor settlement, and poor drainage system (including the choke korle lagoon). The area is connected to the few railway network system in the country and is the home of one of the exquisite hotels in the country, the Zeus. The peoples are basically made up of Ga's and few mixed tribes from all corners of the country. Figure 1 shows a digitize map of Alajo and its surroundings.  Fig 2. Spatial and Non-Spatial data of Alajo GIS is an important tool in planning emergency situations of any magnitude that need critical analysis. One of the most important skills in this field is the basic ability to visualize and depict spatial information that is the ability to read and draw maps. The basic dimensions of emergencies are time, space, magnitude and intensity. Time is the backbone of events, the linear measure of their unfolding, whereas geographical space is the medium in which the events take place. Magnitude refers to the physical forces at work, and intensity to the effects and reactions that these forces cause. GIS methods are useful at all stages of the disaster cycle. In mitigation they help indicate where the physical phenomena to be prevented or protected against are located and where to place structural defences. In both mitigation and preparedness, it can help determine the zones of risk and vulnerability. It can also locate resources that are to be used when disaster strikes. In response, GIS is fundamental. To begin with, it is essential to start operations with a good idea of where the boundaries of the incident or disaster area are, and where the greatest damage and most casualties are located. The principle value of GIS systems is their ability to relate datasets to each other in the form of spatially referenced overlays. This enables the emergency planner to call up overlays at will and superimpose them on a screen. The location of hospitals and emergency points can be superimposed on a network of roads in order to calculate the quickest or shortest routes to transport victims from the site of a mass-casualty incident to places where their injuries can be treated. A further advantage of GIS is that it can be updated rapidly. In emergencies, information can be fed into the system as it is received from the field and routes for emergency vehicles can be planned in order to avoid the blockages. Finally, GIS can be used in planning both reconstruction and mitigation efforts after disaster.  Fig 3. A Buffer of the Lagoon Data capture for this project is from a secondary source and existing maps of the alajo area, which was digitized. Manual digitizing of paper maps is one of the main sources of positional error in GIS. The accuracy of data generated by the method of encoding is dependent on many factors, including the scale and resolution of the source map and the quality of the equipment and software being used. Errors can be introduced during the digitizing process by incorrect registration of the map document on the digitizer table or "hand wobble". Published estimates of the accuracy of manual digitizing range from as high as ±0.8mm (Dunn et al, 1990) to as low as ± 0.054mm (Bolstad et al, 1990).These published estimates were ensured for this project. Imagery of some specific locations were also taken and attached to specific features on some of the thematic layers by hotlinks. Attribute data such as population, age and job description of some suburbs were also collected. Figure 2 shows spatial and non-spatial data collected for the project. Spatial Analysis Spatial analysis in GIS can be shown by visualization and also in a Tabular form. Spatial queries were performed once all appropriate thematic layers have been formed. Simple queries were performed to buffer certain areas to extract some information about the buffers created. The river passing through the township was buffered to cover an extent to see its effect should it flood. With the extents indicated the population that could be affected should it flood could now be demarcated to know the houses that will be affected and how they could be evacuated. Figure 3 is a buffer of the Lagoon. Emergency locations have also been indicated to enable easy access. |